Water-soluble polymers have been widely used in various applications, because of the solubility, for example, in detergent compositions, scale inhibitors, dispersants for various inorganic or organic substances, thickeners, cohesive agents, adhesive agents, surface-coating agents, cross-linking agents, and moisturizers. As such water-soluble polymers, polymers produced by polymerizing an unsaturated carboxylic acid monomer such as an acrylic acid or copolymers of such an unsaturated carboxylic acid monomer with another monomer, and graft polymers produced by a graft polymerization of a polyether compound with an unsaturated carboxylic acid monomer such as acrylic acid, have been widely used conventionally. Various amphoteric copolymers having a cationic group and an anionic group in the structure have been recently investigated for exhibition of contradictory properties.
If such a water-soluble polymer is used in water system applications such as detergent compositions, scale inhibitors, and dispersants, needed performances are different from water qualities because the water qualities such as hardness, attributed o the kind of the water source vary by country, region, or the like. Therefore, development of agents sufficiently satisfying needed performances have been needed. If such a water-soluble polymer is used in a water system with high hardness, the polymer is deactivated due to influence of hardness components such as calcium ion, possibly failing to exhibit sufficient detergency, scale inhibiting capability, dispersibility, or the like. Therefore, an agent capable of sufficiently exhibiting such performances even under high hardness conditions has been needed.
With respect to a conventional amphoteric copolymer, disclosed is a hydrophilic amphoteric polymer formed by copolymerizing an anionic monomer having a carboxyl functional group, a cationic monomer having an amino functional group, a nonionic hydrophilic monomer, a hydrophobic monomer, and a crosslinking monomer (for example, referring to Japanese kohyo Publication No. 2002-533537 (page 2)). However, this hydrophilic amphoteric polymer has room for improvement in order to sufficiently exhibit performances such as detergency even under high hardness conditions and thereby to be useful in much more applications, particularly in water system applications such as detergent composition.
With respect to an antibacterial composition containing an amphoteric copolymer, disclosed is an amphoteric copolymer obtained by using methoxy polyethylene glycol monomethacrylate having an ethylene oxide unit, 2-acrylamide methylpropanesulfonic acid, and dimethylaminoethyl methacrylate in the molar ratio of 1:1:1 (for example, referring to WO 2004/100666 (page 33, Example 25, page 55). However, this copolymer has room for improvement in order to be economically more excellent and preferable, for example, in water system applications such as detergent composition.